The voltage-dependent anion channel (VDAC) mediates trafficking of small molecules and ions across the eukaryotic outer mitochondrial membrane. There are three isoforms that have distinct reported interactions with small molecules and proteins. These include pro- and anti-apoptotic members of the Bcl-2 family, and the different isoforms of VDAC have been implied to play roles in apoptosis, such as formation or inhibition of the mitochondrial exit channel. Recently, we obtained NMR assignments and determined the solution structure of human VDAC-1 in detergent micelles (Hiller et al., 2008). VDAC has been known for thirty years and numerous reports of interactions and functional aspects have been reported. With the recent NMR characterization of VDAC-1 we are now in a position to validate these reports and elucidate the function of the channel. The goal of the proposed research is to study the structure, interactions and function of VDAC isoforms. We will pursue the following specific aims: 1. Compare structure and interactions of VDAC-1 in LDAO micelles and phospholipids nanodiscs to assess differences between micelle and bilayer environments. 2. Determine the structure of VDAC-2, which contains an N-terminal extension and has reported functions distinct from VDAC-1. 3. Determine the membrane/micelle-bound structures of Bcl-2 type proteins and study VDAC complexes. 4. Characterize complexes of VDAC with the porin PorB from pathogenic bacteria. PUBLIC HEALTH RELEVANCE: We will study the solution structure of the human voltage-dependent anion channel (VDAC) in the membrane mimicking phospholipids nanodiscs and compare it with our recent structure obtained in LDAO micelles. We will also determine the structure of the VDAC-2 isoform, which has been shown to stabilize an inactive form of the Bak protein and may play a crucial role in controlling the onset of apoptosis. We also will investigate interactions of VDAC with Bcl-2-type proteins, bacterial pathogens and small molecules.